I agree with BoxtheFox. Dorsoduro is a lovely area and many Venetians live there. Restaurant prices are lower and also a better selection of dishes. The very touristy areas have a limited menu...lots and lots of pizza, pasta and not much else (fine for the first couple of days but a bit sickening after that). In quieter areas you will also avoid the tour groups stampeding around en masse after the lady holding up the red scarf!
Three day pass for vaporetto (water bus) is good value at €22 as you will use it a good bit getting to see the sights. I think a single journey on the grand canal without the ticket is €5 so it all adds up.